Curve modifier, deformation only on Z axis
Array a Z deformed panel

No, the Curve modifier has no option for that yet.

The trick you can go for at the moment is to Shear your panel and set up an array modifer that not only offest on the X axis, but also in the Z of the right amount to build a seamsless mesh.

Luckily stairs usually have steps that are evenly spaced on Z, so the linearity of the height growth imposed by the usage of the Array modifier should not be a problem in this case.

The curve is now defining only the path of the rail on plan:





Note for example that in the picture there the tile is romboid shaped, not squared shaped.